Arizona Gov. Janice Brewer has signed a law providing strong new restrictions on the use of so-called "seclusion rooms" in schools – closet-sized rooms where children with behavioral disabilities such as autism were being locked up as punishment.

"It is chilling to imagine an Arizona school child being shut away in a padded room, no larger than a closet, for hours on end," Brewer said after signing the law Friday. "There has to be a better way."

With the new law, Arizona will join more than 30 other states that impose rules on the restraint of students in public schools.

The use of tiny, windowless seclusion or isolation rooms in American classrooms was one focus of an ABC News investigation that aired on "Nightline" and "World News With Diane Sawyer" in November. The report found that seclusion was one of a range of harsh techniques being used in some American schools to restrain unruly students suffering from autism or other disabilities.

In addition to the controversial use of seclusion rooms, school officials around the country have been employing a wide array of methods to restrain behaviorally disabled children that range from sitting on them, to handcuffing them, even jolting them with an electric shock at one specialized school. Thousands of autistic and disabled schoolchildren have been injured and dozens more have died after being physically restrained by poorly trained teachers and school aides, ABC News found.

The new Arizona law prohibits schools from using confinement on children unless their parents specifically consent to that form of discipline. Brewer called the measure "a starting point" in helping insure children are not harmed in school.

"Our goal must be to insure Arizona children – especially those with special needs – are treated in a way that provides for both their safety and dignity," she said.

The sponsor of the legislation, Ariz. state Rep. Kelly Townsend, said she considers the measure effectively a ban on the use of the isolation rooms.

"The parent now can decide if this kind of discipline is okay for their child and it gives them the option to opt out," Townsend said. "I trust the parents are not going to permit this."

A vocal advocate for the new law was Leslie Noyes, the mother of a seven-year-old boy in Phoenix, Arizona who secretly videotaped the padded room in her son's school after he had been left there for the better part of a school day. She says she later learned he had been held in the room 17 times – though the school disputes that number, saying he was there three times.

"I was disgusted," Noyes told ABC News. "There was one time that I know he was placed in the room a little after 10 a.m. He was there until the school day ended at 3:30 p.m. They brought him lunch in there. He ate it on the floor. He had urinated on the floor. They wouldn't let him out to use the bathroom."

Officials from the Deer Valley Unified School District where Noyes' son went to school said that, because of the pending lawsuit, they could not respond to questions about the case. But in general, spokeswoman Heidi Vega said, seclusion is "the last method of behavior management schools use with a student."

"Our staff is fully trained on non-violent crisis intervention and puts student safety first at all times. The safety of all students is important and remains a top priority," she said.

Rep. George Miller, a California Democrat, proposed national legislation that would create a uniform standard on restraint for the nation's schools – legislation that has failed to even receive a committee vote over the past three years.

Until recently, Miller said, no organization even knew the number of deaths that were occurring on school grounds. He said several advocacy groups spent years tried to assess the toll.

The Coalition Against Institutionalized Child Abuse, an advocacy group, used public records to tally 75 child deaths between 1988 and 2006 that stemmed from the improper use of restraints. A California disability rights organization, Protection and Advocacy, Inc., counted 39 deaths in just that state between 1999 and 2007, all resulting from the use of seclusion or behavioral restraints. A 2009 study by federal auditors reported hundreds of instances between 1990 and 2009 where improper restraint led to injuries, and another study that same year, by the National Disability Rights Network, chronicled dozens of specific cases of young children, many of them autistic, being suffocated or badly injured while being improperly restrained.

There is also little known about how many schools, in how many states, utilize isolation rooms, Miller said. As part of its investigation, ABC News interviewed school children who described the experience of being locked in a seclusion booth as the stuff of nightmares.

"It was dark, there's no windows, you're just stuck in there the whole day," Jordan, an 11-year-old Pennsylvania student, told ABC News. "You felt scared and upset and you were already angry… Even for the bravest kids in the world, it's still really scary."

Hope Kirsch, an Arizona attorney who is representing the Noyes family in their case against the local school district, said she believes the new law will serve as an important first step in ending the use of seclusion rooms in her state.

"This is a victory for parents whose children are victims of this barbaric procedure," Kirsch said. "We would like to see seclusion rooms closed down. The efforts of the Noyes family and Rep. Kelly Townsend, along with Governor Brewer signing the bill, have paved the way toward the ultimate goal of eradicating this inhumane treatment of the most vulnerable population."